Optical fibers have been used in internal wiring of apparatus in the vicinities of ordinary homes with the advance of FTTH (Fiber to the Home) in recent years, so that there is a remarkably increasing demand for optical communication. With the advance of optical communication in such circumstances, there is an increasing demand for a multi-core ribbon-like optical fiber core assembly using a plurality of optical fiber tape cores such as 4 cores, 8 cores, 12 cores, 16 cores, 24 cores or 32 cores.
A ribbon-like optical fiber core assembly has been used widely in indoor wiring or internal wiring of apparatus as well as used in an optical cable.
The ribbon-like optical fiber core assembly is used in various forms as follows. In one of the forms, the ribbon-like optical fiber core assembly may be connected to a multi-core connector provided at a terminal in indoor wiring or internal wiring of apparatus. In another form, the ribbon-like optical fiber core assembly may be separated into single cores at an end of the ribbon-like optical fiber core assembly and fanned out (FO) so that the single cores are connected to single-core connectors respectively. In a further form, the ribbon-like optical fiber core assembly is separated into single cores and the single cores may be then rearranged in the form of a tape.
For example, as one form of the multi-core ribbon-like optical fiber core assembly, a thin ribbon-like optical fiber core assembly capable of achieving a multi-core structure has attracted public attention.
In the related art, as shown in FIG. 13A, there is a ribbon-like optical fiber core assembly molded in such a manner that a batch coating layer 6 of a UV-curable resin or a thermoplastic resin is formed on outer circumferences of a plurality of optical fiber cores 2 arranged planarly in a row.
On the other hand, as shown in FIG. 13B, there has been proposed a ribbon-like optical fiber core assembly formed in such a manner that a plurality of optical fiber cores 2 are arranged in parallel without any contact and integrated into one body by a batch coating layer 6 with a varied thickness so that the ribbon-like optical fiber core assembly can be cut at a thin portion of the batch coating layer 6 so as to be separated into respective optical fiber cores which will be attached to an optical connector or the like (e.g., see Patent Document 1).
As described above, both batch coating removability for performing the work of connecting the optical fiber cores efficiently and single core separability for separating the ribbon-like optical fiber core assembly into single cores to perform terminal processing has been particularly required of the ribbon-like optical fiber core assembly in recent years. Generally, in most cases, wiring is performed on the spot. Accordingly, there is a demand for a ribbon-like optical fiber core assembly which can be separated into single cores efficiently without use of any jig.
(Patent Document 1)
JP-A-11-231183 (page 2, FIG. 1)
Further, as a method for integrating optical fibers as a tape, the following technique has been heretofore disclosed (e.g., see Patent Document 2). As shown in FIG. 26A, a plurality of optical fibers 200 are arranged in a horizontal row to form an optical fiber row 201. As shown in FIG. 26B, at least one thermoplastic film 202 (two thermoplastic films 202 in FIG. 26B) is brought into contact with at least one of upper and lower surfaces of the optical fiber row 201 and heated so as to be melted. As shown in FIG. 26C, melted plastic 203 enters in between optical fiber cores, so that the melted plastic 203 serves as a binder for binding the optical fibers in the form of a ribbon.
On the other hand, the necessity of changing the pitch of arrangement of optical fibers has been heretofore described (e.g., see Patent Document 3).
(Patent Document 2)
JP-A-7-43538 (page 2, FIG. 15)
(Patent Document 3)
JP-A-7-218753
The simplest method for integrating a plurality of optical fibers as a tape is a method using a pressure-sensitive adhesive film. In the method, there is a problem that end surfaces of the tape after integration are sticky or adhesive force of the tape varies with time in accordance with deterioration of a pressure-sensitive adhesive agent used in the pressure-sensitive adhesive film. When the aforementioned thermoplastic film 202 is used or when a heat-curable adhesive agent is used, pressure is applied in order to obtain high adhesive force or fulfill adhesion. If the applied pressure is too high, there is a problem that the pitch of arrangement of the optical fibers 200 is disordered due to displacement of the optical fibers 200 as shown in FIG. 27 or an optical fiber 200a at an end portion jumps out. If the applied pressure is insufficient, lowering of adhesive force is brought about.
Further, optical fibers have been used in internal wiring of apparatus in the vicinities of ordinary homes with the advance of FTTH (Fiber to the Home) in recent years, so that there is a remarkably increasing demand for optical communication. Wavelength division multiplexing (WDM) has been introduced as a transmission technique meeting this demand. WDM is a communication system using one optical fiber for transmitting light having a plurality of wavelengths. With the introduction of this system, there is an increasing demand for a multi-core ribbon-like optical fiber core assembly using a plurality of optical fiber cores such as 4 cores, 8 cores, 12 cores, 16 cores, 24 cores or 32 cores in the form of a tape.
Under such circumstances, the ribbon-like optical fiber core assembly has been also used widely in indoor wiring or internal wiring of apparatus.
As one form of the multi-core ribbon-like optical fiber core assembly, a thin ribbon-like optical fiber core assembly capable of achieving a multi-core structure has attracted public attention.
In the related art, as shown in FIG. 41A, there is a ribbon-like optical fiber core assembly molded in such a manner that a batch coating layer of a UV-curable resin or a thermoplastic resin is formed on outer circumferences of a plurality of optical fiber cores 302 arranged planarly in a row. In the related art, as shown in FIG. 41B, there is also a ribbon-like optical fiber core assembly molded in such a manner that the batch coating layer is covered with a tension member k, which is a reinforcing fiber, according to necessity and further covered with a polyvinyl chloride (PVC) resin composition 316.
As shown in FIG. 41C, there has been further proposed a ribbon-like optical fiber core assembly formed in such a manner that a plurality of optical fiber cores 302 are arranged in parallel without any contact and integrated into one body by a batch coating layer 403 so that the pitch of arrangement of the optical fiber cores 302 is made coincident with the pitch of arrangement of photo acceptance elements or terminals of an optical connector to which the optical fiber cores 302 will be attached (e.g., see Patent Document 1).
In this example, adhesion of the tape material to the coatings of the cores needs to be kept high while the lubricity of a surface of the tape material is kept though the tape material is made of one material. Accordingly, there is a problem that selection of the material is limited strictly.
Both batch coating removability for performing the work of connecting the optical fiber cores efficiently and single core separability for separating the ribbon-like optical fiber core assembly into single cores to perform terminal processing are required of the ribbon-like optical fiber core assembly. These two requirements often impose two antithetical characteristics on the coating material. To simultaneously obtain the two antithetical characteristics, there has been further proposed a technique in which pull-out force between a glass fiber and a protective coating layer and adhesive force between the protective coating layer and a batch coating layer are defined as described in JP-A-2000-155248 (e.g., see Patent Document 4).
(Patent Document 4)
JP-A-2000-155248 (paragraphs 30 to 36)
In the case of indoor wiring or internal wiring of apparatus, it is particularly important to take measures against fires. There is an increasing demand for an optical fiber cable having flame retardancy to prevent the spread of the fire.
Two methods are known for making such an optical fiber cable flame-retardant. One of the two methods is a method in which a flame retardant material is used as a coating material per se of the optical fiber cable so that an optical fiber core is coated with the flame retardant material. The other method is a method in which the circumference of the optical fiber cable is covered with a flame retardant material in the condition that the structure of the optical fiber cable per se is left as it is.
The two methods, however, have problems respectively. In the former method, flame retardancy is given to the coating material included in the optical fiber cable. The translucent property of the flame retardant material is however generally not good. For example, the related-art ribbon-like optical fiber core assembly is often molded in such a manner that optical fiber cores are coated with an ultraviolet-curable (UV-curable) resin which is a non-flame-retardant material. If a flame retarder is added to the ultraviolet-curable (UV-curable) resin, transmission of ultraviolet rays is suppressed to make it difficult to cure the UV-curable resin.
For this reason, the ultraviolet-curable resin popularly used cannot be used as the coating material included in the optical fiber cable, so that reduction in production efficiency is unavoidable.
In the latter method, the structure of the optical fiber cable per se is left as it is. For this reason, the total size inevitably increases, so that the method is unsuitable for wiring in a narrow space such as internal wiring of apparatus.
Also a ribbon-like optical fiber assembly (ribbon type optical fiber assembly) faces the same situation as described above.
Generally, the ribbon-like optical fiber assembly uses a structure in which the circumferences of a plurality of single optical cores arranged in parallel are covered with a batch coating layer (tape layer).
When the ribbon-like optical fiber assembly needs to be made flame-retardant, two methods are conceived in the same manner as in the single-core optical fiber cable. One of the two methods is a method in which a flame retardant material is used as the material of the coating or tape layer so that the optical fiber cores are covered with the flame-retardant material. The other method is a method in which the circumference of the ribbon-like optical fiber assembly is further covered with a flame retardant material in the condition that the structure of the ribbon-like optical fiber assembly per se is left as it is.
Like the case of the single-core optical fiber cable, in the former method, if a flame retarder is added to the coating, for example, made of a UV-curable resin in order to obtain flame retardancy, transmission of ultraviolet rays is suppressed to make it difficult to cure the UV-curable resin.
In the latter method, if the ribbon-like optical fiber assembly is coated with a flame retardant material, the total thickness increases so that adverse influence on reduction in size and diameter of apparatus is unavoidable.